Dynamic Fracture Behaviors of Selected Aluminum Alloys Under Three-point Bending

The dynamic fracture behaviors of the extruded 2024-T4 and 7075-T6 aluminum alloys are investigated by using an instrumented drop tower machine. The specimens are made from a 25 mm diameter extruded circular rod. The dynamic three-point bending tests of each alloy are carried out at different impact velocities. The initiation fracture toughness and average propagation fracture toughness of 2024-T4 and 7075-T6 are determined at different loading rates. The results show that both the initiation toughness and the propagation toughness increase with the loading rate. Further, the difference between the fracture toughness behaviors of 2024-T4 and 7075-T6 is found to be dependent on the variation of fracture mechanism. The comprehensive fractographic investigations of the fracture surfaces clearly demonstrate that the fracture mode of 2024-T4 is predominantly transgranular fracture with high density small-sized dimples, and the fracture mode of 7075-T6 is mainly intergranular fracture with many intermetallic particles in the bottom of voids located in the fracture surface.